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Paging Doctor Dog

Marine is an 8-year-old female black lab. She is substantially more cuddly than a colonoscopy. But she's just about as good at detecting colon cancer.

The dog's Japanese owner and trainer, Yugi Satoh, has been teaching her to sniff out cancer cells since 2005. Marine is trained to sniff at bags containing breath samples from humans, then sit down in front of the sample that smells like cancer. No one knows exactly what chemical signature the dog is smelling, but Satoh says Marine has detected diseases as diverse as lung, breast, prostate, pancreatic and ovarian cancer.

In a new study, Marine sniffed human stool samples in addition to breath samples. She was first given samples from patients with colon cancer and told to find a match. Sniffing breath samples from 306 people, 48 of whom had colon cancer (as diagnosed by a colonoscopy), the dog correctly identified 91% of the cancer patients. With stool samples, she picked out 97% of the cancer patients. And she correctly ignored 99% of the samples from healthy patients.

It may seem incredible, but disease-sniffing dogs aren't new to science. A British charity called Cancer and Bio-detection Dogs trains dogs of various breeds to sniff out bladder cancer, and they've published the research to back up their claims. They also train dogs to live with diabetics; when a dog smells that its owner is having a hypoglycemic crisis, it runs to fetch the insulin kit. Marine, though, may have drawn the best disease detecting assignment--what do dogs love more than sniffing poop?

Author Hideto Sonoda says Marine was also able to pick out samples from patients with stomach, breast and prostate cancer when told to search for the colon cancer smell, though these data aren't included in the paper. This implies that various cancers share the same smell. To find out whether the cancerous smell comes from the presence of a new odor or the absence of a healthy odor, the researchers mixed together stool samples from healthy subjects and cancer patients. The dog still identified the mixed samples as cancerous, suggesting that cancer does have a signature scent.

It would be impractical to bring in dogs and their trainers for routine medical tests, the authors say. But they hope that further research will help them find the exact molecule that causes the cancer smell. Tests for this molecule could then detect cancer in its early stages.

This isn't Marine's first time in the news, by the way. In 2008, when she was already proving her prowess at sniffing out cancer cells, Yugi Satoh decided to have the dog cloned by a South Korean firm called RNL Bio. The firm had previously been hired by a California woman who paid them $150,000 to clone her beloved dead pit pull, Booger.

Four cloned puppies came from Marine's cells. RNL Bio named them Marine-R, Marine-N, Marine-L, and Marine-S (the S stands for...South Korea?) Two of the puppies were to be given to labs, and the other two would be sold.

All dogs are excellent sniffers, so it seems likely that a dog's training is more relevant to its disease-detecting abilities than whether it has the exact genome of another disease-sniffing dog. But wherever those puppies are now--hunting diseases or not--odds are, they're happily sniffing poop.

Clarification: A person having a hypoglycemic attack needs sugar, not insulin. The dog in the diabetes example would fetch its owner's insulin kit so the owner could check her blood sugar levels. (Thanks, Brenna!)

Who's Inkfish?

Hi, I'm Elizabeth. I live near Boston and work as the editor of MUSE, a kids' science magazine that's not otherwise related to this blog. My writing has also appeared in National Geographic, Slate, and other publications. Read more here.